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Operational Amplifier (Op Amp) Basics, Uses and Applications

更新時間: 2023-10-05 17:20:18

Operational amplifiers, commonly known as op-amps, are essential components in modern electronics, finding applications in many fields. Whether you are a student, electronics enthusiast, or professional in the industry, understanding the basics of op amps is essential. This comprehensive guide will explore the fundamentals of op-amps, covering everything from their definition to their different types, advantages, and disadvantages. By the end of this article, you will have a solid understanding of op-amps, enabling you to select and use them effectively for your electronic projects or professional applications. So, let's dive in and explore the exciting world of op-amps!
What is an Operational Amplifier?
An operational amplifier(op-amp) is an electronic circuit component that amplifies and outputs an input signal. It is a key building block in analogue circuits and is widely used in various applications, including signal conditioning, filtering, and active filtering.

The op-amp is a high-gain electronic amplifier with a differential input and a single-ended output. It can amplify various signals, from DC to high frequency, and perform various mathematical operations on the input signal, such as addition, subtraction, integration, and differentiation.

Basic Operational Amplifiers
At operational amplifier core parts, it consists of a differential amplifier, which amplifies the voltage difference between two input signals, and a gain stage, which amplifies the output of the differential amplifier to a desired level. The output of an op-amp is typically hundreds or thousands of times larger than the input signal and can be either positive or negative, depending on the phase of the input signals.

Op amps have a high input impedance, which makes them suitable for use with high-impedance sensors and other low-current sources. They are also known for their low output impedance, which allows them to drive loads such as speakers or motors. Op amps are a building block for many electronic circuits capable of amplifying small signals to much larger levels, making them a key component in many applications.

Characteristics
High Gain
One of the main characteristics of an operational amplifier (op-amp) is its high gain. Gain is the measure of the amplification capability of an amplifier. An op-amp can provide a gain of several hundred thousand times, which makes it an ideal choice for amplifying weak signals. An op-amp's gain depends on the amplifier's open-loop gain (AOL), which is the gain of the op-amp without any feedback. The AOL of the op-amp is very high, and it can be adjusted to a particular gain by adding feedback to the amplifier.

High Input Impedance
Another important characteristic of op-amps is their high input impedance. Input impedance measures the ease with which a circuit accepts an incoming signal. The input impedance of an op-amp is typically several megaohms, which means that it presents a very high impedance to the signal source. This high input impedance ensures that the op-amp does not load down the signal source and can work with various signal sources, including high-impedance sensors, without affecting their output.

The high input impedance of an op-amp is essential in applications such as photodiode amplifiers and signal conditioning circuits.

Low Output Impedance
Output impedance is the measure of the resistance offered by the output of the amplifier to the load. A low output impedance is essential because it enables the op-amp to deliver maximum power to the load without any signal attenuation. The low output impedance of an op-amp is achieved by using an output buffer amplifier that can drive the load impedance with a high current.

Schematic diagram of an operational amplifier
High Bandwidth
Bandwidth measures the range of frequencies over which an amplifier can provide amplification. The high bandwidth of op-amp results from its high gain and fast response time. The high gain ensures the signal is amplified to a high level, while the fast response time enables the op-amp to amplify signals with high-frequency components.

High Common-Mode Rejection Ratio (CMRR)
CMRR measures an op-amp's ability to reject common-mode signals, which are signals that are present on both the op-amp's input terminals. A high CMRR ensures that the op-amp responds only to differential signals, which are the signals between the op-amp's input terminals. The high CMRR of an op-amp is achieved by using a differential amplifier at the input stage that can reject common-mode signals.

This characteristic of an op-amp is essential in applications such as instrumentation amplifiers and signal-processing circuits.

Low Offset Voltage
The offset voltage is the voltage at the amplifier's output when both input terminals are at zero volts. The offset voltage results from mismatches in the op-amp's internal components. A low offset voltage is essential in applications that require accurate amplification of small signals, such as strain gauge amplifiers and thermocouple amplifiers.

Low Noise
Low noise is another important characteristic of operational amplifiers. Noise refers to any unwanted signal that is added to the desired signal. In an ideal amplifier, no noise would be added to the output signal, but in reality, all amplifiers will add some amount of noise to the signal. Low noise is important for applications where the amplified signal is very small, such as in medical devices or precision measurement equipment. The noise performance of an op-amp is typically measured in terms of its noise density, which is the amount of noise contributed by the amplifier per unit of bandwidth. Op-amps can also be designed with additional features such as chopper stabilization or auto-zeroing to reduce noise and offset voltage.

The high gain, high input impedance, low output impedance, high bandwidth, high common-mode rejection ratio, low offset voltage, and low noise are some of the most important characteristics of operational amplifiers. The choice of which op-amp to use in a given application will depend on the specific requirements of the circuit, such as the desired gain, bandwidth, and noise performance.

Pin Configuration
Let's take the popular LM741 op-amp as an example further to understand the pinout and functions of each pin. The LM741 has eight pins, each serving a specific function in the overall operation of the op-amp.

LM741

Pin 1: Offset null pin, which is used to adjust the input offset voltage of the op-amp.
Pin 2: Inverting input pin, where the input signal concerning ground is applied.
Pin 3: Non-inverting input pin, where the input signal is applied.
Pin 4: Voltage supply pin for the op-amp.
Pin 5: Offset null pin for some op-amps, but it is not used in the LM741.
Pin 6: Output pin, where the amplified output signal is obtained.
Pin 7: Voltage supply pin for the op-amp.
Pin 8: Compensation pin, which is used to improve the stability of the op-amp.

Understanding the pinout of an op-amp is crucial in designing and utilizing op-amp circuits. The LM741 serves as an excellent example of the various functions that each pin can perform.

Types
Voltage Feedback Op Amp
A voltage feedback op is widely used due to its high gain, high input impedance, and low output impedance. The voltage feedback op amp has a differential input stage with a high gain output stage. The differential input stage is responsible for the high input impedance of the voltage feedback op amp. The ratio of the output voltage to the input voltage determines the gain of a voltage feedback op amp. This makes the voltage feedback op amp ideal for amplifying signals, as it can provide a large output signal even for small input signals.

Current Feedback Op Amp
The current feedback op amp is another type of operational amplifier that is used in high-speed applications. A current amplifier characterizes this op-amp as the input stage, which provides a low input impedance and high bandwidth. The current feedback op amp can amplify high-frequency signals without introducing phase shifts, making it useful for amplifying signals in video and RF applications. Unlike the voltage feedback op amp, the current feedback op amp has a flat gain response at high frequencies, making it an ideal choice for high-frequency applications.

Differential Op Amp
The differential op amp is an op-amp with two input terminals and a single output terminal. The differential input terminals amplify the voltage difference between the two input signals. This op-amp type is commonly used in applications requiring high common-mode rejection, such as in instrumentation amplifiers, where the differential input signal is very small compared to the common-mode signal. The differential op amp can also be used as a comparator in circuits that require precise signal detection.

Instrumentation Op Amp
The instrumentation op amp is a type of op-amp used in applications requiring a high level of accuracy, stability, and noise reduction. This op amp is designed to amplify signals from transducers, such as pressure sensors and thermocouples, and can provide a high gain with low noise and low offset voltage. The instrumentation op-amp also has a high common-mode rejection, making it ideal for applications that require the measurement of small signals in the presence of a large common-mode signal.

Programmable Op Amp
The programmable op-amp is an op-amp that allows for customization of the gain, bandwidth, and other characteristics of the amplifier circuit. This op-amp has an external digital-to-analogue converter (DAC) that can program the op-amp's characteristics. The programmable op-amp is useful in applications requiring a high level of flexibility, such as audio and signal processing applications.

Power Op Amp
The power op amp is an op-amp designed to deliver a high output power while maintaining high accuracy and stability. This op-amp type is used in power supply applications, motor control circuits, and audio amplifiers. The power op-amp can deliver high currents and voltages while maintaining low distortion and high efficiency. It is also designed to handle high temperatures and to operate reliably in harsh environments.

Applications
Signal Conditioning
Audio Amplification
Voltage Regulation
Analog-to-Digital Conversion
Oscillators
Active Filter
Comparators
Instrumentation Amplifiers
Function Generators

Advantages and Disadvantages of Op Amp
Like any other electronic component, operational amplifiers have advantages and disadvantages. Here are some of the advantages and disadvantages of op-amps.
Advantages:
High gain
High input impedance
Low output impedance
High bandwidth
High common-mode rejection ratio
Low offset voltage
Low noise
Disadvantages:
Limited power supply voltage range
Limited output voltage swing
Slew rate limitations
Limited frequency response

What are Operational Amplifiers used for?
Operational amplifiers have many applications in electronics and are used in a wide range of circuits.

Some of the most common applications of op-amps include amplifying signals, active filtering, signal conditioning, oscillators, comparators, and voltage regulators. Op amps are also used in instrumentation and control circuits, audio and medical equipment, and various industrial and scientific applications.

They are often used as basic building blocks for designing complex circuits and systems. The versatility and flexibility of op amps make them a popular choice for many applications, and they continue to be widely used in modern electronic design.

How to choose an Operational Amplifier?
Choosing the right operational amplifier involves considering factors such as the required gain, bandwidth, input/output impedance, voltage offset, and noise, as well as the temperature range, power supply voltage, and package type, and comparing those specifications against the requirements of the specific application, and then find an op-amp that meets those specifications and is suitable for your specific application.

Here are some popular operational amplifiers that you can consider or choose from:
LM741, LM358, LM386, TL081, TL082
TL084, AD620, AD623, AD712, AD826
Each of these op amps has its own set of specifications, features, and characteristics, so it is important to choose the one that best fits the requirements of your application. Factors to consider include the required voltage and current range, input and output impedance, gain, bandwidth, noise, and power supply voltage. It would help if you also considered whether you need a single, dual, or quad op-amp package and a surface-mount or through-hole package. By carefully considering these factors and comparing the specifications of different op amps, you can choose the one that will give you the best performance for your particular application.

Final Words
Operational amplifiers are essential in modern electronics, with a wide range of applications, from simple circuits to complex systems. By understanding the basics of op-amps, you can unlock the full potential of these versatile electronic components. Whether you're a hobbyist, student, or professional, mastering op amps can open up new possibilities and lead to exciting projects and innovations. So, whether you're building a simple amplifier or a complex control system, an op-amp is an invaluable tool that can help you achieve your goals and bring your ideas to life.

Operational Amplifier FAQ
What is the difference between an inverting and a non-inverting op-amp configuration?
In an inverting op-amp configuration, the input signal is applied to the inverting input (-) of the op-amp. At the same time, the feedback resistor is connected between the output and the inverting input. The output signal is inverted relative to the input signal. In a non-inverting op-amp configuration, the input signal is applied to the op-amp's non-inverting input (+). At the same time, the feedback resistor is connected between the output and the non-inverting input. The output signal is in phase with the input signal.

What is the gain in op-amp circuits?
Gain is the amount by which an op-amp amplifies an input signal. It is typically expressed in decibels (dB) units or as a simple ratio of output voltage to the input voltage. The gain of an op-amp circuit can be adjusted by changing the values of the feedback resistors.

What is the difference between an op-amp and a comparator?
An op-amp is designed to amplify voltage signals, while a comparator is designed to compare two voltage signals and output a digital signal based on their relative magnitudes. A comparator has a very high gain but does not have the linear response or low output impedance of an op-amp.

What is the difference between a single-supply and dual-supply op-amp?
A single-supply op-amp is powered by a single voltage source, while both positive and negative voltage sources power a dual-supply op-amp. Single-supply op-amps are often used in battery-powered or portable devices, while dual-supply op-amps are more commonly used in AC-powered devices.